Maintaining network availability for wireless clients in a wireless local area network

ABSTRACT

In an example embodiment, there is described herein a technique that provides network availability to wireless clients (e.g., wireless clients running mission critical applications such as voice applications or medical devices) when a portions of a network is unavailable, such as when performing an image upgrade. One or more access points are switched to a standalone mode of operation, for example an AP that can operate using HREAP (Hybrid Remote Edge Access Point) mode, for maintaining network availability while a portion of the network is unavailable.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/608,114 filed Dec. 7, 2006.

BACKGROUND

During image upgrades, Access Points (APs), and/or switches for theaccess points are rebooted after an image download is completed. Forexample, a LWAPP (Lightweight Access Point Protocol) switch upgrades itsimage, the switch and its associated access points reboot, causingdowntime to the entire network. This causes loss of connectivity for aperiod of time, which is not acceptable for wireless clients servicingvoice applications or mission critical applications such as medicalapplications.

OVERVIEW OF EXAMPLE EMBODIMENTS

The following presents a simplified summary of the invention in order toprovide a basic understanding of some aspects of the invention. Thissummary is not an extensive overview of the invention. It is intended toneither identify key or critical elements of the invention nor delineatethe scope of the invention. Its sole purpose is to present some conceptsof the invention in a simplified form as a prelude to the more detaileddescription that is presented later.

In an example embodiment, there is described herein an apparatuscomprising a controller with logic operable to control the operation ofa plurality of access points. The controller is configured to select aselected access point to operate in a standalone mode. The controller isfurther configured to send a signal to an unselected access point of theplurality of access points to direct the unselected access point tosignal a wireless client to associate with the selected access point.The controller sends a signal to the unselected access point to switchthe unselected access point to an inoperative mode.

In an example embodiment, there is described herein an apparatuscomprising a wireless transceiver, a communication interfacecommunicatively coupled to a distribution network and a controller foroperatively controlling the wireless transceiver and the communicationinterface. The controller is responsive to a signal received by thecommunication interface to initiate an image upgrade to select awireless client associated with the wireless transceiver to signal theselected wireless client via the wireless transceiver to associate withanother access point.

In an example embodiment, there is disclosed herein a method comprisingselecting a selected access point from a plurality of access points foroperating in standalone mode and directing a selected wireless client toassociate with the selected access point. The method further comprisesperforming an image update to the plurality of access points that arenot operating in standalone mode. The method suitably comprisesdirecting the wireless client to associate with one of the plurality ofaccess points that are not in standalone mode after the image update hasbeen performed to the plurality of access points that are not operatingin standalone mode. An image update is performed on the selected accesspoint.

Still other objects of the present invention will become readilyapparent to those skilled in this art from the following descriptionwherein there is shown and described a preferred embodiment of thisinvention, simply by way of illustration of at least one of the bestmodes best suited to carry out the invention. As it will be realized,the invention is capable of other different embodiments and its severaldetails are capable of modifications in various obvious aspects allwithout departing from the invention. Accordingly, the drawing anddescriptions will be regarded as illustrative in nature and not asrestrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings incorporated herein and forming a part of thespecification, illustrate examples of the present invention, andtogether with the description serve to explain the principles of theinvention.

FIG. 1 illustrates an example embodiment of a network with a singlecontroller configured for maintaining availability for wireless clients.

FIG. 2 is illustrates an example embodiment of a network with a multiplecontrollers configured for maintaining availability for wirelessclients.

FIG. 3 illustrates an example embodiment of an access point configuredfor maintaining availability for wireless clients.

FIG. 4 illustrates an example of a computer system for implementing anexample embodiment.

FIG. 5 illustrates an example methodology for providing highavailability for wireless clients.

DESCRIPTION OF EXAMPLE EMBODIMENTS

This description provides examples not intended to limit the scope ofthe invention, as claimed. The figures generally indicate the featuresof the examples, where it is understood and appreciated that likereference numerals are used to refer to like elements.

In an example embodiment, there is described herein a technique thatprovides network availability to wireless clients (e.g., wirelessclients running mission critical applications such as voice applicationsor medical devices) when portions of a network are unavailable, such aswhen performing an image upgrade. One or more access points are switchedto a standalone mode of operation, for example an AP that can operateusing HREAP (Hybrid Remote Edge Access Point) mode, for maintainingnetwork availability.

The controller can be aware of mission critical and voice clients basedon WMM/CAC usage and/or a special IE can be employed for identifyingmission critical devices, such as medical devices. The controllerdirects the mission critical and voice clients to roam (associate) withany access points operating in standalone mode.

In an example, embodiment, after the unavailable portion of the networkagain becomes available (e.g., the access points or other controllershave completed their image updates and rebooted), the controller directsthe wireless access points associated with the standalone access pointsto move the wireless clients to other access points so that thestandalone access points can be upgraded. Once the mission critical andvoice wireless clients have moved off the standalone access points, theaccess points can perform the image upgrade, reboot and resume operationon a non-standalone mode.

In an example embodiment, the controller can perform an image updatewhile the standalone access points maintain network availability to themission critical and voice clients. Once the controller has completedthe upgrade, the access points can return to a non-standalone mode.Optionally, after the controller has performed the upgrade, thecontroller can direct select one or more access points to remain inoperation while another group of access points performs the upgrade andreboot. After the upgraded access points reconnect to the controller,the selected one or more access points can then be upgraded.

In an example embodiment, where multiple controllers are employed, eachcontroller having an associated plurality of access points, a controllerand its associated access points can remain in service while othercontrollers and their associated access points switch to an inoperablemode. For example, while performing an image upgrade, a second set ofcontrollers and its associated access points remain operational while afirst set of controllers and their associated access points perform theupgrade. The first set of controllers direct mission critical wirelessclients and voice clients to associate with access points associatedwith the second set of controllers. After the mission critical wirelessclients and voice clients have roamed (associated) to access pointsbelonging to the second set of access points, the first set ofcontrollers and/or their associated access points download the image,reboot and return to an operational mode. After the first set of clientsreturn to an operational mode, the second set of controllers directtheir associated access points to move the mission critical and voiceclients to access points associated with the first set of controllers.After the wireless client have roamed (associated) to the first set ofcontrollers, the second set of controllers and/or their associatedaccess points download the image for upgrade, reboot and return to anoperational mode.

FIG. 1 illustrates an example embodiment of a network 100 with a singleWLAN controller 102 configured for maintaining availability for wirelessclients. Controller 102 is communicatively coupled by a distributionnetwork 104 (e.g., a wired network such as an Ethernet or IP Network ora wireless network such as a mesh network or a combination or wired andwireless networks) to access points 106, 107, 108. Access points 106,107, 108 have an associated coverage area, 116, 117, 118 respectively.Controller 102 comprises logic operable to control the operation ofaccess points 106, 107, 108. “Logic”, as used herein, includes but isnot limited to hardware, firmware, software and/or combinations of eachto perform a function(s) or an action(s), and/or to cause a function oraction from another component. For example, based on a desiredapplication or need, logic may include a software controlledmicroprocessor, discrete logic such as an application specificintegrated circuit (ASIC), a programmable/programmed logic device,memory device containing instructions, or the like, or combinationallogic embodied in hardware. Logic may also be fully embodied assoftware.

When WLAN controller 102 decides to switch a first set of access pointsto a non-operational mode (e.g., to perform an image upgrade), switchcontroller 102 selects a second set of access points to remain in astand alone operational mode. As used herein, a non-operational mode isa mode wherein an access point is unable to provide service for awireless client during the duration of image upgrade and a stand aloneoperational mode is a mode wherein the access point can provide serviceto a wireless client in the absence of the controller. For example, WLANcontroller 102 can decide to switch access points 106, 108 into anon-operational mode to perform an upgrade and select access point 107to remain in operational mode. When the WLAN controller 102 isupgrading, WLAN controller 102 can signal access point 107 to switch toa standalone mode, enabling access point 107 to continue operating whileWLAN controller 102 and/or access points 106, 108 are non-operational.

WLAN controller 102 determines a wireless client (or a set of wirelessclients) for maintaining network availability while WLAN controller 102and access points 106, 108 are non-operational. WLAN controller 102 candetermine mission critical or voice clients based on any definedcriteria, such as WMM/CAC usage or by determining from an IE associatedwith a wireless client that the wireless client is a mission criticalwireless client (for example a medical device or an emergencycommunication device). Alternatively, WLAN controller 102 can select allwireless clients.

WLAN controller 102 directs access points 106, 108 to signal thewireless clients and/or voice clients (e.g., wireless clients 126, 128)to associate with access point 107. For example, as illustrated in FIG.1, wireless client 126 is initially associated with access point 106 asillustrated by arrow 136 and wireless client 128 is initially associatedwith access point 108 as illustrated by arrow 138. If WLAN controller102 determines that wireless clients 126, 128 are mission criticaland/or voice clients, it can direct them to associate with access point107 as illustrated by arrows 146, 148 respectively. After wirelessclients 126, 128 have moved from access points 106, 108 respectively,WLAN controller 102 can switch itself to non-operational mode for anupgrade and then switch access points 106, 108 to a non-operationalmode.

After access points 106, 108 have switched to a non-operational mode, animage upgrade or other maintenance can be performed on them. While theimage upgrade or other maintenance is being performed, access point 107maintains connectivity between distribution network 104 and wirelessclients 126, 128. WLAN controller 102 can signal access points 106, 108to reboot (restart) after image upgrade or other maintenance isperformed. Alternatively, access points 106, 108 can automaticallyreboot, if desired, when ready to return to service.

As WLAN controller 102 and/or access points 106, 108 return to anoperational mode, WLAN controller 102 can signal wireless access point107 to direct wireless clients 106, 108 to associate with either accesspoint 106 or access point 108. WLAN controller 102 can signal accesspoint 107 to switch to a non-operational mode or reboot for upgrading tothe new image that now exists on the switch/controller 102. WLANcontroller 102 switches access point 107 to non-operational mode afterwireless clients 126, 128 have associated with other access points(e.g., access points 106, 108). Access point 107 can then perform animage upgrade, or other maintenance, and return to an operational modewhen completed. In an example embodiment, access point 107 returns to anoperational mode after a reboot (restart).

In an example embodiment, WLAN controller 102 is configured to determinethe location of wireless clients (e.g., wireless clients 126, 128) formaintaining network availability. WLAN controller 102 selects an accesspoint (e.g., AP 107) for the wireless clients (e.g., wireless clients126, 128) based on the proximity of the selected access point to thelocation of the wireless clients. In the example illustrated in FIG. 1,wireless clients 126, 128 are both within coverage area 117 for accesspoint 107. Thus, WLAN controller 102 can select access point 107 toremain in operation (e.g., in a standalone mode) while WLAN controller102 and/or access points 106, 108 are in a non-operational mode. WLANcontroller 102 signals access points 106, 108 to signal wireless clients126, 128 respectively to associate with access point 107. After WLANcontroller 102 and/or access points 106, 108 return to an operationalmode, WLAN controller 102 can signal access point 107 to have wirelessclients 126, 128 to associate with one of access points 106, 108. Afterwireless clients 126, 128 are no longer associated with access point 107WLAN controller 102 can switch access point 107 to a non-operationalmode.

FIG. 2 is illustrates an example embodiment of a network 200 with amultiple controllers configured for maintaining availability forwireless clients. In this embodiment, there are illustrated two WLANcontrollers 202, 204 coupled to distribution network 206. Access points212, 216 are coupled to WLAN controller 202. Access points 210, 214 arecoupled to WLAN controller 204. A wireless client is initiallyassociated with access point 210 at 220, and subsequently roams to at222 to access point 216 pursuant to a signal from access point 210. Inthis example embodiment the wireless client moves from access point 210on WLAN controller 204 to access point 216 on WLAN controller 202.

In an example embodiment, WLAN controllers 202, 204 and their associatedaccess points switch to a non-operational mode at different times tomaintain network availability. For example, WLAN controller 204 andaccess points 210 and 214 associated with controller 204 can switch to anon-operational mode (e.g., to perform an image update) while WLANcontroller 202 and access point 216 and 212 associated with WLANcontroller 202 remain in an operational mode. Before switching to anon-operational mode, WLAN controller 204 sends a signal throughdistribution network 206 to access point 210 to have a wireless clientassociated with access point 210, illustrated at 220, to roam(associate) with access point 216, illustrated at 222. After thewireless client has roamed, WLAN controller 204 and access points 210and 214 switch to a non-operational mode (e.g., perform an imageupgrade). When WLAN controller 204 and one or more of access points 210,214 return to an operational mode (e.g., after performing a reboot afteran image upgrade), WLAN controller 202 can signal access point 216 tohave wireless client associate with one of the access points 210, 214associated with WLAN controller 204. After the client has roamed to anaccess point associated with WLAN controller 204, WLAN controller 202and access point associated with WLAN controller 202 (which are accesspoints 212 and 216) switch to a non-operational mode.

In an example embodiment, if WLAN controllers 202, 204 need to switch toa non-operational state (for example some maintenance is needed), accesspoints 210, 212, 214, 216 can all be signaled to switch to a standaloneoperation mode (e.g., they will operate without receiving any controlfunctions from their controller). Once access points 210, 212, 214, 216have switched to a standalone mode, WLAN controllers 202, 204 can switchto a non-operational mode. After WLAN controllers 202, 204 have returnedto an operational mode, access points 210, 212, 214, 216 can again beassociated with their respective WLAN controllers 202, 204.

In an example embodiment, WLAN controllers 202, 204 can switch selectedaccess points to a standalone mode (e.g., APs 216, 212), while WLANcontrollers 202, 204 and/or unselected access points (e.g., APs 210,214) switch to a non-operational mode. In an example embodiment, anymission critical, voice clients and/or all wireless clients associatedwith the unselected access points can be signaled to switch to one ofthe selected access points. After WLAN controllers 202, 204 and the APs(e.g., 210, 214) that were switched to a non-operational mode return toan operational mode (e.g., after completing an image upgrade andrebooting), wireless clients (either mission critical wireless clients,voice wireless clients and/or all wireless clients) associated with theselected access points can be directed to roam (associate) with theunselected access points. After the wireless clients roam to theunselected access points, the selected points can then be switched to anon-operational mode.

FIG. 3 illustrates an example embodiment of an access point 300configured for maintaining availability for wireless clients. Accesspoint 300 is suitable to implement the functionality described foraccess points 106, 107, 108 (FIG. 1) and/or access points 210, 212, 214,216 (FIG. 2). AP 300 comprises a wireless transceiver 302 operable forwireless communication. Wireless transceiver 302 may suitably comprisean antenna 301 for transmitting and receiving wireless signals. Wirelesstransceiver 302 can have circuits for amplification,modulation/demodulation, frequency conversion, digital to analog (D/A),analog to digital (ND), etc.

Radio controller 304 is coupled to wireless transceiver 302. Radiocontroller 304 is operative to control the operation of wirelesstransceiver 302. Radio controller 304 comprises logic for performing thefunctionality described herein. Radio controller 304 is configured toacquire data from wireless signals received by wireless transceiver 302.Radio controller 304 is also configured to send data to wirelesstransceiver 302 for wireless transmission.

Distribution network interface 306 is coupled to radio controller 304and is employed to couple AP 300 to a distribution network. Radiocontroller 304 is operative to controls the operation of distributionnetwork interface 206, e.g., distribution network 104 (FIG. 1) or 206(FIG. 2). For example, referring to AP 107 in FIG. 1, wirelesstransceiver 302 is employed for wirelessly communicating with wireless(mobile) clients, such as clients 126, 128 and distribution networkinterface 306 is coupled to network 304 via a coupler 308. If AP 300 iscoupled to the distribution network via a wired connection (e.g.,Ethernet), then coupler 308 could be a wired connection such as anEthernet cable. If AP 300 is coupled wirelessly to the distributionnetwork (e.g., the distribution network is a Mesh network), then coupler308 can be an antenna suitably adapted for sending and receivingwireless signals.

In an example embodiment, radio controller 304 is responsive to a signalreceived by communication interface 308 to initiate an image upgrade toselect a wireless client (not shown) associated with wirelesstransceiver 302 to signal the selected wireless client via wirelesstransceiver 302 to associate with another access point.

In an example embodiment, radio controller 304 selects the wirelessclient based on a wireless multimedia extension associated with thewireless client. In an example embodiment, radio controller 304 selectsthe wireless client based on a call admission control associated withthe wireless client. In an example embodiment, radio controller 304selects the wireless client based on an information element associatedwith the wireless client. The information element can be configured toidentify the wireless client as a high priority client such as a medicaldevice or emergency service device.

In another example embodiment, radio controller 304 selects all wirelessclients associated with wireless transceiver 302.

FIG. 4 illustrates an example of a computer system 400 for implementingan example embodiment. Computer system 400 can suitably be employed forimplementing the functionality of WLAN controller 102 and/or accesspoints 106, 107, 108 (FIG. 1); WLAN controllers 202, 204 and/or accesspoints 210, 212, 214, 216 (FIG. 2); and/or radio controller 304 (FIG.3). Computer system 400 includes a bus 402 or other communicationmechanism for communicating information and a processor 404 coupled withbus 402 for processing information. Computer system 400 also includes amain memory 406, such as random access memory (RAM) or other dynamicstorage device coupled to bus 402 for storing information andinstructions to be executed by processor 404. Main memory 406 also maybe used for storing a temporary variable or other intermediateinformation during execution of instructions to be executed by processor404. Computer system 400 further includes a read only memory (ROM) 408or other static storage device coupled to bus 402 for storing staticinformation and instructions for processor 404. A storage device 410,such as a magnetic disk or optical disk, is provided and coupled to bus402 for storing information and instructions.

An aspect of an example embodiment is related to the use of computersystem 400 for maintaining high network availability for wirelessclients in a wireless local area network (WLAN). According to oneembodiment of the invention, maintaining high network availability forwireless clients in a WLAN) is provided by computer system 400 inresponse to processor 404 executing one or more sequences of one or moreinstructions contained in main memory 406. Such instructions may be readinto main memory 406 from another computer-readable medium, such asstorage device 410. Execution of the sequence of instructions containedin main memory 406 causes processor 404 to perform the process stepsdescribed herein. One or more processors in a multi-processingarrangement may also be employed to execute the sequences ofinstructions contained in main memory 406. In alternative embodiments,hard-wired circuitry may be used in place of or in combination withsoftware instructions to implement the invention. Thus, embodiments ofthe invention are not limited to any specific combination of hardwarecircuitry and software.

The term “computer-readable medium” as used herein refers to any mediumthat participates in providing instructions to processor 404 forexecution. Such a medium may take many forms, including but not limitedto non-volatile media, volatile media, and transmission media.Non-volatile media include for example optical or magnetic disks, suchas storage device 410. Volatile media include dynamic memory such asmain memory 406. Transmission media include coaxial cables, copper wireand fiber optics, including the wires that comprise bus 402.Transmission media can also take the form of acoustic or light wavessuch as those generated during radio frequency (RF) and infrared (IR)data communications. Common forms of computer-readable media include forexample floppy disk, a flexible disk, hard disk, magnetic cards, papertape, any other physical medium with patterns of holes, a RAM, a PROM,an EPROM, a FLASHPROM, any other memory chip or cartridge, a carrierwave as described hereinafter, or any other medium from which a computercan read.

Computer system 400 also includes a communication interface 418 coupledto bus 402. Communication interface 418 provides a two-way datacommunication coupling to a network link 420 that is connected to adistribution network 422. For example, communication interface 418 maybe an integrated services digital network (ISDN) card or a modem toprovide a data communication connection to a corresponding type oftelephone line. As another example, communication interface 418 may be alocal area network (LAN) card to provide a data communication connectionto a compatible LAN. Wireless links may also be implemented. In any suchimplementation, communication interface 418 sends and receiveselectrical, electromagnetic, or optical signals that carry digital datastreams representing various types of information.

Network link 420 typically provides data communication through one ormore networks to other data devices. Computer system 400 can sendmessages and receive data, including program codes, through associatednetwork(s), network link 420, and communication interface 418.

In view of the foregoing structural and functional features describedabove, a methodology 500 in accordance with various aspects of thepresent invention will be better appreciated with reference to FIG. 5.While, for purposes of simplicity of explanation, the methodology 500 ofFIG. 5 is shown and described as executing serially, it is to beunderstood and appreciated that the present invention is not limited bythe illustrated order, as some aspects could, in accordance with thepresent invention, occur in different orders and/or concurrently withother aspects from that shown and described herein. Moreover, not allillustrated features may be required to implement methodology 500 inaccordance with an aspect the present invention. Embodiments of thepresent invention are suitably adapted to implement methodology 500 inhardware, software, or a combination thereof.

Starting the description of methodology at 500 at 501, at 502 adetermination is made as to whether an image upgrade or maintenance isneeded for a network device (e.g., a WLAN controller and/or AP). If animage upgrade is not needed, or no maintenance is needed (NO), thenmethodology stops at 518. However, if at 502 it is determined that animage upgrade or maintenance is needed (YES), at 503, the location ofone or more mission critical wireless clients and/or wireless voiceclients is determined. Mission critical clients can be identified byassociated WMM usage or IE associated with the wireless client. Forexample an IE can identify a client as a medical device, security deviceor an emergency communication device. Voice clients can be identified byCAC usage. In an alternative example embodiment, the location of allwireless clients can be determined. Any technique can be used fordetermining the location of the wireless clients such as Received SignalStrength Intensity (RSSI), Angle of Arrival (AOA), or Global PositioningService (GPS).

At 504, one or more access points are selected to operate in astandalone mode, such as HREAP. In an example embodiment, the accesspoints are selected based on proximity to the mission critical and/orvoice wireless clients to ensure service to these clients.

At 506, the mission critical and/or voice wireless clients are directedto roam (associate) to one of the selected access points. A signal canbe sent to the access point where the mission critical and/or voiceclients are currently associated to direct them to roam (associate) to aselected access point. Optionally, the message directing the missioncritical and/or voice client to roam can specify which access point toroam.

At 508, an image update (or other maintenance) is performed on theunselected access points. In an example embodiment, the unselectedaccess points switch to a non-operational mode (e.g., they stopservicing wireless clients), download the new image, install the newimage, and then restart (reboot). After the restart, the unselectedaccess points are again in an operational mode (e.g., they are nowcapable of servicing wireless clients).

At 510, the wireless clients (either the mission critical, voice and/orall wireless clients) are moved off the selected access points. A signalcan be sent to the wireless clients providing a list of access points,or specifying an access point, available for servicing the wirelessclient.

At 512, the selected access points perform the image upgrade. Theselected access points can verify that all mission critical, voice,and/or all wireless clients have roamed to another access point beforeinitiating the image upgrade. In an example embodiment, the imageupgrade includes switching to a non-operational mode, downloading andinstalling the new image, and restarting (rebooting). After rebooting,all of the access points will have been upgraded, while maintainingnetwork availability. At 516 normal operation is restored and at 518 theprocess is completed.

In the aforementioned descriptions, the example embodiments performedtwo image upgrades, first the unselected access points and/orcontrollers and/or then the selected access points and/or controllers.However, those skilled in the art can readily appreciate that any sizegrouping can be selected for performing network maintenance and/or imageupgrades and the algorithm can be repeated as often as desired toupgrade the entire network. For example, for a very busy network, maybeonly twenty percent of the access points can be down at any one time inorder to maintained sufficient network connectivity to the missioncritical and/or voice clients. In this example the algorithm can berepeated five times, (e.g., twenty percent of the access points areremoved from service at any one time, thus five iterations would beperformed to upgrade all access points.

What has been described above includes example implementations of thepresent invention. It is, of course, not possible to describe everyconceivable combination of components or methodologies for purposes ofdescribing the present invention, but one of ordinary skill in the artwill recognize that many further combinations and permutations of thepresent invention are possible. Accordingly, the present invention isintended to embrace all such alterations, modifications and variationsthat fall within the spirit and scope of the appended claims interpretedin accordance with the breadth to which they are fairly, legally andequitably entitled.

1. An apparatus, comprising: a controller with logic operable to controlthe operation of a plurality of access points communicating with aplurality of mobile wireless clients in a network; wherein thecontroller is configured to determine a set of mobile wireless clientsselected from the plurality of wireless clients for maintaining networkavailability, the set of mobile wireless clients selected from one of agroup consisting of mission critical wireless clients and wireless voiceclients; wherein the controller is configured to determine a location ofa member of the set of mobile wireless clients for maintaining networkavailability; wherein the controller is configured to select a selectedaccess point to operate in a standalone mode, the selected access pointis selected in accordance with a proximity of the selected access pointto the location of the member of the set of mobile wireless clients formaintaining network availability; wherein the controller is configuredto send a first signal to the selected access point directing theselected access point to operate in the standalone mode; wherein theselected access point is responsive to the first signal to operate inthe standalone mode; wherein the controller is configured to send asecond signal to an unselected access point of the plurality of accesspoints to direct the unselected access point to communicate a message tothe set of wireless clients for maintaining network availability, themessage comprising data directing the set of wireless clients toassociate with the selected access point operating in the standalonemode; and wherein the controller is configured to send a third signal tothe unselected access point to switch the unselected access point to anon-operational mode.
 2. An apparatus according to claim 1, furthercomprising the controller is configured to signal the unselected accesspoint to perform an image upgrade while the unselected access point isin the non-operational mode.
 3. An apparatus according to claim 1,further comprising the controller is configured to signal the unselectedaccess point to perform a restart while the unselected access point isin the non-operational mode.
 4. An apparatus according to claim 1,further comprising: the controller is responsive to detecting that atleast one unselected access point of the plurality of access points hasreturned to an operational mode to signal the selected access point tosignal the set of mobile wireless clients to associate with one of theat least one unselected access point; and the controller is responsiveto detecting that at least one unselected access point of the pluralityof access points has returned to an operational mode to signal theselected access point to switch to the non-operational mode.
 5. Anapparatus according to claim 1, wherein the controller is configured toselect the set of mobile wireless clients for maintaining networkavailability based on a wireless multimedia extension associated withthe set of mobile wireless clients.
 6. An apparatus according to claim1, wherein the controller is configured to select the set of mobilewireless clients for maintaining network availability based on a calladmission control associated with the set of mobile wireless clients. 7.An apparatus according to claim 1, wherein the controller is configuredto select the set of mobile wireless clients for maintaining networkavailability based on an information element associated with the set ofmobile wireless clients.
 8. An apparatus according to claim 7, whereinthe information element identifies at least one mobile wireless clientof the set of mobile wireless clients as a medical device.
 9. Anapparatus according to claim 1, further comprising: a second controller,wherein the selected access point is associated with the secondcontroller; and wherein the second controller and the selected accesspoint remain in an operational mode while the unselected access point isin the non-operational mode.
 10. An apparatus according to claim 9,further comprising: the second controller is responsive to determiningat least one unselected access point of the plurality of access pointshas returned to an operational mode to signal the selected access pointto signal the set of mobile wireless clients to associate with a one ofthe at least one unselected access point that has returned to anoperation mode; and the second controller is responsive to signal theselected access point to switch to the non-operational mode.
 11. Anapparatus according to claim 10, wherein the unselected access point isconfigured to perform an image upgrade and initiate a reboot while inthe non-operational mode, and the second controller and selected accesspoint are configured to perform an image upgrade and initiate a rebootafter switching to the non-operational mode.
 12. An apparatus,comprising: a wireless transceiver for communicating with a plurality ofmobile wireless clients; a communication interface communicativelycoupled with an associated distribution network; and a controller foroperatively controlling the wireless transceiver and the communicationinterface; wherein the controller determines a set of mobile wirelessclients selected from the plurality of wireless clients for maintainingnetwork availability, the set of mobile wireless clients selected fromone of a group consisting of mission critical wireless clients andwireless voice clients; wherein the controller is configured todetermine a location of a member of the set of wireless client formaintaining network availability; wherein the controller is responsiveto a signal identifying a selected access point for receiving an imageupdate to determine a second access point that is within a proximity tothe location of the member of the set of wireless clients formaintaining network availability associated with the selected accesspoint, to send a message to the member of the set of wireless clientsfor maintaining network availability associated with the selected accesspoint to roam to the second access point.
 13. An apparatus according toclaim 12, wherein the controller selects a mobile wireless client formaintaining network availability based on a wireless multimediaextension associated with the mobile wireless client.
 14. An apparatusaccording to claim 12, wherein the controller selects a mobile wirelessclient for maintaining network availability based on a call admissioncontrol associated with the mobile wireless client.
 15. An apparatusaccording to claim 12, wherein the controller selects a mobile wirelessclient for maintaining network availability based on an informationelement associated with the mobile wireless client.
 16. An apparatusaccording to claim 15, wherein the information element identifies themobile wireless client for maintaining network availability as a medicaldevice.
 17. A method, comprising: determining a set of mobile wirelessclients selected, from the plurality of mobile wireless clients formaintaining network availability, the set of mobile wireless clients formaintaining network availability selected from a group consisting ofmission critical wireless clients and wireless voice clients;determining a location of a selected member of the set of mobilewireless clients for maintaining network availability; selecting aspecified access point from a plurality of access points for operatingin standalone mode in accordance with a proximity of the specifiedaccess point to the location of the selected member of the set of mobilewireless clients for maintaining network availability; communicating, tothe selected member of the set of mobile wireless clients formaintaining network availability a message comprising datarepresentative of the specified access point, the data representative ofthe specified access point directing the selected member of the set ofmobile wireless clients for maintaining network availability toassociate with the specified access point; performing an image update anunselected access point belonging to the plurality of access points thatis not operating in the standalone mode; directing the member of the setof mobile wireless clients for maintaining network availability toassociate with the unselected access point after the image update hasbeen performed to the unselected access points; and performing an imageupdate to the specified access point after directing the member of theset of mobile wireless clients for maintaining network availability toassociate with the unselected access point.